1. Field of the Invention
The present invention relates to a temperature estimating apparatus for an internal combustion engine which estimates the temperature of an exhaust device such as a catalyzer arranged in an exhaust system through calculations.
2. Description of the Related Art
Conventionally, one type of known temperature estimating apparatus mentioned above thermodynamically calculates the temperature of an exhaust device in an exhaust system of an internal combustion engine. More specifically, the exhaust device is thermodynamically modeled to estimate a heat exchanging state between the exhaust device and exhaust gases to calculate the temperature of the exhaust device. The temperature of the exhaust device is estimated in this manner because a detecting device such as a temperature sensor is relatively expensive to manufacture, in addition to its low reliability. Thus, the temperature estimating apparatus avoids such problems in order to increase reliability in detecting the temperature and to reduce the manufacturing cost.
The conventional temperature estimating apparatus could fail to correctly calculate the temperature of the exhaust device when the internal combustion engine is started under a low temperature condition for the reasons set forth below. When the internal combustion engine is started at a low ambient temperature which causes a cold exhaust pipe in an exhaust system, the saturated steam pressure of exhaust gases becomes lower associated with a reduction in the temperature of the exhaust gases passing through the exhaust device, thereby possibly resulting in condensation of moisture contained in the exhaust gases on wall surfaces of the exhaust device. In this event, heat applied from the exhaust gases to condensed water is consumed for a phase change from the condensed water to stream as latent heat of vaporization, so that the exhaust device does not change in temperature. It is therefore necessary to calculate the temperature of the exhaust device in consideration of the influence of the condensed water thus produced. However, because the amount of condensed water thus produced, and a situation in which the condensed water is produced depend on external environmental conditions and an operating condition of the internal combustion engine upon starting, it is difficult to correctly reflect the influence of condensed water to the thermodynamic model as a result of difficulties in measurements and calculations. Consequently, the temperature of the exhaust device can be incorrectly calculated when the internal combustion engine is started under low temperature conditions.
The present invention has been made to solve the problem as mentioned above, and it is an object of the present invention to provide a temperature estimating apparatus for an internal combustion engine which is capable of correctly calculating the temperature of an exhaust device even when the internal combustion engine is started under low temperature conditions.
To achieve the above object, the present invention provides a temperature estimating apparatus for an internal combustion engine arranged in an exhaust system of the internal combustion engine for estimating a temperature of an exhaust device for purifying exhaust gases through calculations. The temperature estimating apparatus includes an operating condition detecting means for detecting an operating condition of the internal combustion engine, including a state of intake air; a humidity detecting means for detecting the humidity of exhaust gases; and a device temperature calculating means for calculating the temperature of the exhaust device in accordance with the detected operating condition of the internal combustion engine and the detected humidity of the exhaust gases.
As described above, when the temperature of an exhaust device is calculated by a technique of thermodynamically modeling the exhaust device, condensation of moisture in exhaust gases could cause an incorrectly calculated temperature of the exhaust device when the temperature of the exhaust system is low as a result of a low external temperature. In contrast, the temperature estimating apparatus for an internal combustion engine of the present invention calculates the temperature of the exhaust device in accordance with a detected operating condition of the internal combustion engine, including the state of intake air, and the humidity of exhaust gases in the exhaust system. Therefore, even when condensation is highly likely to occur as a result of a low external temperature, the temperature of the exhaust gas is calculated only when exhaust gases have a low humidity and are free from condensation, thereby making it possible to calculate the temperature of the exhaust device while avoiding the influence of the condensation. As a result, the temperature estimating apparatus for an internal combustion engine of the present invention can correctly calculate and estimate the temperature of the exhaust device even when the internal combustion engine is started under a low temperature condition.
Preferably, the temperature estimating apparatus for an internal combustion engine further includes condensation determining means for determining whether or not condensation occurs within the exhaust system in accordance with the detected humidity of the exhaust gases, wherein the device temperature calculating means calculates the temperature of the exhaust device further in accordance with a result of determination made by the condensation determining means.
According to this preferred embodiment of the temperature estimating apparatus for an internal combustion engine, the temperature of the exhaust device can be correctly estimated, while securely avoiding the influence of condensation, by calculating the temperature of the exhaust device only when no condensation occurs within the exhaust system in accordance with the result of determination made by the condensation determining means.
Preferably, the temperature estimating apparatus for an internal combustion engine further includes calculation start timing determining means for determining a timing for start calculating the temperature of the exhaust device by the device temperature calculating means in accordance with the result of determination made by the condensation determining means.
According to this preferred embodiment of the temperature estimating apparatus for an internal combustion engine, because the device temperature calculating means can start the calculation of the temperature of the exhaust device when no condensation occurs within the exhaust system, it is possible to start calculating the temperature of the exhaust device at an optimal timing.
Preferably, in the temperature estimating apparatus for an internal combustion engine, the device temperature calculating means calculates an upstream temperature at a location of the exhaust system upstream of the exhaust device in accordance with the operating condition of the internal combustion engine and the humidity of the exhaust gases, and calculates the temperature of the exhaust device in accordance with the calculated upstream temperature.
Generally, in the internal combustion engine, the temperature of exhaust gases near an exhaust port can be correctly calculated in accordance with an operating condition of the internal combustion engine. As exhaust gases flow down, heat is lost as a result of heat exchange with the exhaust system. Taking into account these properties, the temperature estimating apparatus for an internal combustion engine of the present invention calculates the upstream temperature at a location of the exhaust system upstream of the exhaust device in accordance with the operating condition of the internal combustion engine and the humidity of exhaust gases, and calculates the temperature of the exhaust device in accordance with the upstream temperature which is calculated based on the more correct temperature of exhaust gases near the exhaust port. Thus, the temperature of the exhaust device can be calculated in consideration of a change in temperature of the exhaust system due to heat exchange with exhaust gases, at a location upstream of the exhaust device, thereby further improving the accuracy of the calculation.
Preferably, in the temperature estimating apparatus for an internal combustion engine, the exhaust device includes a hydrocarbon adsorbent for adsorbing hydrocarbons in exhaust gases.
This preferred embodiment of the temperature estimating apparatus for an internal combustion engine can accurately estimate the temperature of the hydrocarbon adsorbent and accordingly estimate with a high accuracy the adsorption and desorption of hydrocarbons to and from the hydrocarbon adsorbent in accordance with the estimated temperature.
Preferably, the temperature estimating apparatus for an internal combustion engine further includes desorption determining means for determining whether or not hydrocarbons have been completely desorbed from the hydrocarbon adsorbent in accordance with the temperature of the hydrocarbon adsorbent calculated by the device temperature calculating means.
Generally, the hydrocarbon adsorbent has a property of substantially completely desorbing hydrocarbons when it is heated to a predetermined temperature or higher. Therefore, according to this preferred embodiment of the temperature estimating apparatus for an internal combustion engine, it is possible to correctly determine whether or not hydrocarbons have been completely desorbed from the hydrocarbon adsorbent.